Some components of refrigeration compressors are supported by bearings. To achieve reliable operation for long periods of time, bearings, and other compressor components, require lubrication by a lubricant with adequate viscosity. In a refrigeration system, this is provided by the use of a suitable oil. After long periods of compressor non-operation, oil can completely drain from the bearings. If the compressor is started after such a period, the bearings, and or other components, will operate for some period of time with no lubricant, causing metal-to-metal contact between parts . This can result in wear, ultimately shortening the useful life of the compressor. Additionally, in some compressor refrigeration systems, the pressure differential between compressor compartments may be used to develop lubrication flows. In such systems, some time may be required after initial start up to develop pressure differences adequate for establishing lubrication flows. During this time, there is no delivery of oil to the bearings and other components, thereby resulting in their wear.
One method of accomplishing lubrication, shortly before and/or during start up, is by the use of a positive displacement pump (with suitable piping) which is activated prior to start up, thereby drawing lubricant from an oil reservoir and delivering it to the bearings and other components. A positive displacement pump used for this purpose adds its own reliability risk as well as substantial cost. The pump can be of substantial size because it may be required to deliver a significant amount of oil to provide an adequate amount of lubrication to the bearings and other components of the compressor.
Prior to shutdown, pressurized oil, or oil-rich oil-refrigerant solution is isolated from the rest of the refrigeration system in a dedicated accumulator. The isolated oil is at a pressure that is higher than the pressure existing in the bearing cavities and other components at the time of start up and is maintained at this higher pressure by applying a preload on a spring acting on a piston so as to form a spring-driven piston. The spring is preloaded by a pressure differential acting across the piston which is established prior to compressor shutdown. Accumulator pressure loss and accompanying loss of spring preload can occur due to the long term effects of leakage across the piston face and valves during long periods of compressor shutdown. To alleviate this problem, a small, positive displacement pump can be added to the system solely for preloading the spring by delivering pressurized oil to the side of the piston opposite the spring and thereby pressurizing the accumulator chamber acting against the spring.
Preliminary to restarting the refrigeration system, the state of isolation of this pressurized oil is ended by placing the oil in fluid communication with the bearings and possibly other components to be lubricated. Flow of the oil results by virtue of its pressure being higher than the pressure at the bearings and other components as the oil is being expelled from the accumulator by the spring driven piston, thereby accomplishing pre-start lubrication.
It is an object of this invention to provide lubrication shortly before and/or during start up using a pre-charged fluid reservoir.
It is another objective of this invention is to provide and enhance lubrication of compressor components shortly before and/or during start up using a small, inexpensive pump in combination with a pre-charged fluid reservoir.
It is a further object of this invention to provide a method and apparatus for lubrication delivery prior to and/or during start up that is compatible with the normal operation of the lubrication system. These objects, and others as will become apparent hereinafter, are accomplished by the present invention.